GASTRIC-EMPTYING REGULATES THE KINETICS OF NITROGEN ABSORPTION FROM N-15-LABELED MILK AND N-15-LABELED YOGURT IN MINIATURE PIGS

Thirty-six miniature pins divided into two groups of 18 animals were f ed N-15-labeled milk or yogurt. Polyethylene glycol 4000 was added to the diets as a non-absorbable marker of the liquid phase. Animals were slaughtered 1, 2, 4, 8 and 12 h after meal ingestion, and the gastroi ntestinal tract was removed and divided into 10 parts. Polyethylene gl ycol, total nitrogen and N-15 enrichment were measured in the digesta. Both the intestinal delivery of the liquid phase and the nitrogenous fraction of the chyme were delayed more in pigs fed yogurt than in pig s fed milk. No stimulatory effect of diet ingestion on endogenous nitr ogen secretion was found. Both milk proteins and yogurt proteins were highly digestible: 93% of the exogenous nitrogen disappeared 12 h afte r feeding. The kinetics of exogenous nitrogen delivery into the intest ine was correlated (r = 0.999 for milk and r = 0.974 for yogurt) with that of exogenous nitrogen absorption. These results suggest that milk proteins are rapidly absorbed after they reach the intestine. Gastric emptying is a major factor controlling the kinetics of milk nitrogen absorption.